Unveiling low-temperature thermal oxidation growth of W18O49 nanowires with metastable β-W films

With features of innate tunnels and oxygen vacancies derived from a unique geometrical structure and sub-stoichiometric compositions, W18O49 nanowires have been explored as multifunctional materials with diverse applications. Though thermal oxidation offers a facile method to synthesize patterned W18O49 nanowires, the relatively high growth temperature (≳500 °C) hinders their emerging applications in flexible or wearable electronics. In this work, aiming to lower the growth temperature of W18O49 nanowires by thermal oxidation, the temperature and oxygen partial pressure dependent growth has been systematically investigated for both W films and powders. W18O49 nanowires could be steadily obtained with appropriate temperature and oxygen pressure ranges for both cases, while the growth temperature of a W film (metastable β phase dominant) could be much lower than that of W powder (α phase). The structural analysis indicates that metastable β-W is susceptible to oxidation in comparison with α-W and thus generates oxidation-induced chemical compression for nanowire growth. The growth temperature of W18O49 nanowires could be reduced to ca. 400 °C, which paves the way for the in situ patterning of W18O49 nanowires on indium-tin-oxide (ITO) glass substrates and flexible substrates.